In our earlier studies impedance of thawed fish fillets was measured at frequencies from 1 Hz to 1 MHz and results indicated that measurements at frequencies near 1 MHz have a potential to differentiate fillets with different freezing histories. However, as muscle tissue showed anisotropy even at these frequencies, the aim of this study was to evaluate if the measurements at frequencies up to 100 MHz could be better indicators of freezing history. In this study, sea bass fillets were frozen at -20 ºC, stored for 1 or 3 months with constant or fluctuated temperature during storage, and thawed overnight at +6 ºC. The impedance properties, protein solubility, pH, water holding capacity, lipid oxidation and color of the fillets were measured. The HP 4294A Precise LCR meter was used to measure impedance magnitude (|Z|) and phase (φ) at 200 frequencies from 100 Hz to 100 MHz. Needle-type multielectrode array was used to interface the sample to the instrument. Impedance measurements and especially phase measurements showed the potential of detecting the differences among the fillets at frequencies from 1 to 3 MHz and from 40 to 100 MHz. Compared to measurements at lower frequencies, anisotropy of muscle tissue was reduced. Further studies will focus on other fish species and different fishery products.

Food processing technology